Current broadband access technology mainly includes copper line access technology and optical access technology. An access network implemented with optical access technology is called an Optical Access Network (OAN). Passive Optical Network (PON) technology is an optical access technology with a point to multipoint transmission. A Giga-bit PON (GPON) is an evolution based on PON, which meets a higher rate requirement.
FIG. 1 is a diagram showing the structure of a PON system. The PON system mainly includes three parts, which are an Optical Line Terminal (OLT), an Optical Distribution Network (ODN) and an Optical Network Unit (ONU).
The OLT is used to provide a Network Side Interface (SNI) for the OAN, and to connect one or a plurality of ODNs. The ODN is used to distribute the downlink data from the OLT to each ONU via optical lines, and to make the uplink data from the ONU converge upon the OLT. The ONU is used to provide a User-side Network Interface (UNI), and to connect the ODN. An ONU is called an ONT if it also provides a function such as a user port for Ethernet or a user port for Plain Old Telephone Service (POTS). For the convenience of description, the ONU and the ONT are generally called the ONT.
In a GPON system, the OLT controls the ONT by means of an ONT Management and Control Interface (OMCI). Similar to ordinary service data, data in the OMCI is encapsulated by an OMCI Adapter into Asynchronous Transfer Mode (ATM) cell or Giga-bit PON Encapsulation Method (GEM) data blocks for transmission.
Service flows with GEM encapsulation are multiplexed by a Giga-bit PON Encapsulation Method PORT (GEM PORT) inside a Transmission Container (T-CONT). Each GEM PORT is assigned a GEM PORT identification (GEM PORT-ID). Service flows with ATM encapsulation are multiplexed by a Permanent Virtual Path/Permanent Virtual Channel (PVP/PVC) inside the T-CONT. Each PVP/PVC is assigned a Virtual Path Identification/Virtual Channel Identification (VPI/VCI). A Dynamic Bandwidth Assignment (DBA) Control module in a GPON Transmission Convergence (GTC) layer assigns dynamical bandwidths for each ONT by monitoring and managing all T-CONTs.
Descriptions are made below for GEM encapsulation, but all the descriptions also apply to ATM encapsulation.
FIG. 2 is a diagram showing the structure of the ONT bearing Ethernet services. The ONT includes a Media Access Control (MAC) Bridge Module and an 802.1p Priority Mapping Module. The MAC Bridge Module may alternatively be a plain Ethernet Port Adapter Module.
In the ONT, the MAC Bridge Module realizes the function of Ethernet switching, and supports the access to a plurality of Ethernet interfaces. The MAC Bridge Module receives Ethernet frames from external Ethernet ports P1, P2 and P3, and switches the Ethernet frames by an internal Ethernet switching function to the internal Ethernet port P0 connected with 802.1p Priority Mapping Module. The 802.1p Priority Mapping Module receives Ethernet service flows from the internal Ethernet port, and maps Ethernet frames with different 802.1p priorities to different GEM PORTs, or maps Ethernet frames with a plurality of 802.1p priorities to one GEM PORT.
The operation of 802.1p priority mapping is specifically realized by means of OLT scheduling. The OLT, via the OMCI channel, instructs the ONT, to map Ethernet frames with different 802.1p priorities to corresponding GEM ports. In the OMCI protocol, various data of the OLT managing ONT is abstracted into a protocol-independent Management Information Base (MIB), and the basic information element for the MIB is the Manage Entity (ME). Based on the ONT configurations of various types, the OMCI defines each ME with which the OLT controls ONT. The ONT realizes the configuration management functions of each ME under the control of the OLT.
According to the current GPON technical standards, the ONT supports only the function of mapping Ethernet frames to GEM PORT according to the 802.1p priorities, but does not support the function of mapping to different GEM PORT according to other message characteristics. The other message characteristics mentioned here include: a Virtual Local Area Network (VLAN) ID, a Different Service Code Point (DSCP) field of the IP layer, an IP or MAC source address, an IP or MAC destination address, a protocol type, a TCP/UDP port number, etc. If Ethernet frames can not be mapped to different GEM PORT according to arbitrary message characteristics, it is not possible to provide specific QoS services via a single T-CONT for Ethernet frames with arbitrary message characteristics. Therefore, existing standards can not satisfy the requirements in case of precise service classification and QoS guarantee.
Additionally, in the GPON system, each ONT may be accessed by one or a plurality of multicast users. Referring to the diagram illustrating the multicast service transmission in FIG. 3, the OLT performs authentication processing after it receives an IGMP request message from a multicast user, and requests a multicast program stream specified by the user from a network side multicast source server when the authentication is successful. The specified multicast program stream is sent by the multicast source server to the OLT, and the multicast service flow is copied by the OLT to each multicast user via each ONT. In the meantime, the OLT periodically sends IGMP inquiry messages to the multicast user to detect whether the multicast user is on line. The IGMP request message and the IGMP inquiry message may each be called an IGMP control message. In the current GPON technology standard, the IGMP control messages are usually transmitted being mixed with data service such as that for surfing Internet. Because the priority of the data service such as that for surfing Internet is low, and therefore the QoS of IGMP control messages may not be guaranteed, thereby directly affecting the performance of multicast services.
The above is only a description of the transmission of IGMP control messages, but in fact, the same problems exist for other uplink control messages. The other uplink control messages include: control messages for Ethernet bearing PPP protocol (PPPoE), control messages for Dynamic Host Configuration Protocol (DHCP), control messages for Session Initialization Protocol (SIP), etc.